In the recent past there has been a significant increase in the use of aluminum especially in the beverage industry where the employment of aluminum cans has skyrocketed. Over the years there has been a persistent effort by industry to come up with scrap aluminum reclamation apparatus and associated methods that will allow for the continuous recycling of aluminum cans. Typically these recyling approaches have contemplated the reclamation of any and all forms of aluminum scrap, whether the scrap be aluminum cans in a shredded condition or aluminum scrap which has been generated by any one of a number of other manufacturing operations.
The aluminum scrap reclamation industry has always been vexed by the problem of getting submerged in molten metal light weight, thin pieces of scrap that inherently tend to float on the surface of the molten metal into which they must be submerged in order to be most efficiently melted. This general problem of overcoming the inherent tendency of materials to float on the surface of a fluid medium in which the floating materials are to be mixed is faced in fluid mixing environments other than scrap aluminum and molten metal. The apparatus and method to be described hereinafter will find utilization in these other environments.
The advance state-of-the-art in the technical area of aluminum scrap reclamation is best exemplified by the Claxton Pat. Nos. 4,322,245 ('245) and 4,386,764 ('764) which are directed to a method and apparatus for submerging, entraining, melting and circulating a metal charge in a molten media.
Prior to the inventions just noted, most scrap reclamation systems had unwisely included an independent pump to get the molten metal to circulate through the system. The invention of the above noted '245 and '764 patents employed a rotating impeller configured to cause the formation of a vortex in the molten media which in turn caused a charge of scrap to be initially entrained in the media and drawn in a vertically downward direction whereupon the impeller caused the molten media and charge to change from a vertically downward direction to a horizontally outward direction. This impeller action thereby caused the charge to be completely entrained in the molten media and delivered into a molten media circulation path that in turn delivered the charge entrained in the molten media for subsequent heating, further melting and recirculation. The pumping recirculation rate has proved in practice to be exceptional. It has been discovered, however, that because of system parameters, i.e. volume of scrap, heating bay size etc. that this exceptional pump recirculation rate was, in some instances, excessive. As is presently understood in this art useful vortex generation is tied in part to the rotational rate of the impeller. It is not difficult to appreciate that for systems that employ the impeller of the type shown in the '245 and '769 patents that each system has inherently an optimum capacity. What happens when you want to double the rate of charge into the system? In order to maintain the desired vortex, the rate of impeller rotation must be increased substantially, however, the increase in impeller rotation rate causes an already exceptional recirculating pumping rate to become extraordinary. This extraordinary recirculating pumping rate is far greater than necessary to thoroughly melt entrained scrap in the system. The invention to be described more fully hereinafter provides a solution to these just enumerated problems by providing a method and apparatus that effectively result in the partition of the vortex submergence function and the recirculating pumping function.
There have been others that have sought to perfect vortex generation in a scrap aluminum reclamation such as in the van Linden Pat. No. 4,128,415 which has an impeller 70 that employs two sets of blades 71 and 100, which impeller must cooperate with connical wall of the charging bay. While van Linden does appear to recognize that the formation of the vortex 90 is enhanced by the upper blades 100, the impeller structure requires that fluid be drawn upwardly through a central opening in the bottom plate 70 of impeller 100. The subject invention will be seen to distinguish itself over van Linden in both apparatus and method.
Another patent of interest is the Ostberg U.S. Pat. No. 3,554,518 which is directed to improving the reaction between two liquids of different specific gravities. The impeller structure of Ostberg is intended to ensure that there is provided a turbulent flow of the two liquids in a reaction zone. While Ostberg does show in FIG. 3 an embodiment of his invention that includes a dished shaped impeller with vanes 15 disposed on an upper surface of the impeller, which vanes redirect the flow of the slag layer 3, it should be abundently clear that the impeller of Ostberg contains two pumps that cooperate to agitate in a turbulant fashion the fluids involved, rather than as in the invention to be described herein the formation of a vortex for the entrainment of material while simultaneously pumping the fluid into a recirculation path. Another impeller configuration intended to agitate the fluid medium it is in, is that of Foster as shown in U.S. Pat. No. 2,660,525. The Foster impeller while employing a pair of disk shaped plates disposed in a parallel fashion to agitate the medium, requires an independent pump to move the medium through the system.
It is recognized that in the fan impeller art there are centrifugal fans of the type shown by the Watkins Pat. No. 1,447,916 which suggests that the impeller may be so configured such that there is provided an inlet opening at its center of rotation and an outlet to provide an inlet and outlet which redirect the flow vertically backward. The invention to be described hereinafter provides for vortex generation and charge entrainment in a fluid media while simultaneously establishing the pumping of the fluid media into a circulation path. These just enumerated features and advantageous functions are not suggested by Watkins.